The present invention relates to portable temperature maintenance systems and particularly to portable refrigeration systems which are adapted for transportation to and use with chambers and particularly insulated chambers such as insulated cargo containers.
Previously considerable difficulty had been experienced in maintaining a desired temperature in insulated chambers, particularly cargo containers, where the chamber is not provided with its own temperature regulating equipment. Many perishable products are shipped over long distances and must be stored for brief periods of time while in transit. This is a particularly serious problem where air freight is involved. Air cargo containers do not include tbheir own temperature regulating systems because the added weight would make them prohibitively expensive. The cargo does not generally require refrigeration while airborne. Perishable cargos such as fruits or other produce may be damaged very quickly, however, when the cargo container is parked for a few hours outside the aircraft on the tarmac where the temperature may exceed 100 degrees Fahrenheit. It is often not economical to provide a fixed storage unit for air freight cargo containers at the airport. Often the capacity, particularly at smaller airports, provided by the storage facility is not utilized much of the time. While the storage facility is standing empty, the temperature must be maintained at the desired level in expectation of the next shipment which may need it. Also, the location of such a storage facility must be in the cargo handling areas so it is subject to damage from forklifts and other handling equipment. In general, stand alone temperature regulated storage units are uneconomical except at the very largest airports and then only at those terminals where there is a continuous demand for such facilities. It is usually not economical to transport cargo containers several miles to the other side of a large airport just to use a cold storage facility for a few hours. The cost of transporting cargo containers from the point where they are unloaded to the storage facility and loadintg them into that facility can quickly become prohibitive.
Previous expedients which have sought to overcome these and other difficulties of the prior art have been generally unsatisfactory. One previous expedient involved the use of a refrigeration unit which was designed to be transported to an insulated cargo container and strapped over the opening of the container. An opening in one side of the refrigeration unit was intended to match the side of and seal with the opening in the cargo container. Inside the refrigeration unit was equipment which generated cold air. This prior expedient was difficult to use. The presence of irregularities in both the surfaces upon which the container and refrigeration unit rest as well as irregularities in the opening of the container itself, make it difficult to achieve an adequate seal.